This invention relates to a three-phase matrix converter with diodes, providing controlled armature and field currents to a DC motor.
Matrix converters have been developed primarily to be used for direct AC to AC power conversion; typically, conversion is from multiple phase input power to multiple phase output power, where more than two phases are involved at the input and output. Due to recent advancements in semiconductor technology, matrix converters have become competitive for three phase to DC regenerative converters employing semiconductor switches and anti-parallel diodes.
FIG. 1 illustrates a known matrix converter 6 with three input phases and three output phases, which comprises a topology of choice for AC regenerative drives, such as are used in elevators. In FIG. 1, a conventional insulated gate, bipolar transistor bridge 7 receives three phases of input power on lines 8 from a conventional LC filter 9 which is connected to the three phases R, S, T of AC power mains 10. Each of the switches S11-S33 within the bridge 7 comprises two sets, each set including an insulated gate bipolar transistor (IGBT) and antiparallel diode, such that each switch is bidirectional. As is known, by selective operation of the switches S11-S13, S21-S23, S31-S33 within the bridge 7, the bridge provides three-phases of voltage A, B, C on bridge output lines 45-47 to a three-phase induction motor (IM) 50.
By connecting switches Sij, where i indicates the output phase 1, 2 or 3 and j indicates input phase 1, 2 or 3, output voltages are created in a pulse width modulation fashion from input voltages. Switches Sij are turned on and off in such a way that locally averaged output voltages and input phase current are sinusoidal. Two switches in the same output phase are not turned on at the same time, since that would create a short circuit between two input phases. Current in any of the output phases cannot be interrupted without providing an alternate path. Operation and methods for controlling matrix converters are treated extensively in the following literature: C. L. Neft and C. D. Schauder, xe2x80x9cTheory and design of a 30-hp matrix converter,xe2x80x9d IEEE Trans. Ind. Applicat., vol. 28, no. 3, pp. 546-551, 1992; L. Hube and D. Borojevic, xe2x80x9cSpace vector modulated three-phase to three-phase matrix converter with input power factor correction,xe2x80x9d IEEE Trans. Ind. Applicat., vol. 31, pp. 1234-1246, November/December 1995; P. Nielsen, F. Blaabjerg, J. K. Pedersen, xe2x80x9cNew Protection Issues of a Matrix Converter: Design Considerations for Adjustable-Speed Drivesxe2x80x9d, IEEE Transactions on Industry Application, pp. 1150-1163, Volume 35 Number 5, September/October 1999.
In FIG. 2, only two poles of the bridge 7, S11-S13 and S3-S33, are utilized to provide two poles of DC voltage A, B on a pair of lines 52, 53 to the armature of a DC motor 55. Although the range of output frequencies for matrix converters includes zero Hertz, the use of a three phase-to-three phase matrix converter for a DC drive, as illustrated in FIG. 2, is not practical since it provides power only to the armature circuit, and provides no power to the field circuit. This problem can be overcome by using a three-phase to four-phase matrix converter as illustrated in FIG. 3, with alternate output phases connected to the armature and to the field respectively. FIG. 3 differs from FIG. 2 by providing second and third poles, S21-S23 and S41-S43, within a bridge 7a to provide connections to the nodes 1, K of the field 57 of the DC motor 55 on related lines 58, 59. The circuit and its controller, however, are more complex and costlier than the circuit of FIG. 1, and it is not a practical solution.
In the elevator industry, there are many existing elevator installations with DC motors, and it would be beneficial to be able to drive those motors more effectively with matrix converters, both in new equipment and as a retrofit upgrade. It would also be advantageous to utilize essentially identical converter apparatus for both AC and DC installations.
Objects of the invention include provision of a matrix converter which is readily adapted for use either with AC or DC motors; provision of means for readily adapting a three-phase to three-phase matrix converter for use in driving DC motors; a low cost and efficient method of upgrading existing DC elevator drive motors for control by matrix converters; and a relatively simple, cheap and easily used adaptation of a three-phase-to-three-phase matrix converter for use driving DC motors.
This invention is predicated in part on the recognition of the fact that a DC motor driven with three-phase power by a regenerative matrix converter need not have bidirectional currents in the field winding, and therefore does not require a conventional three-switch matrix converter pole for powering the DC motor field winding.
According to the present invention, two outputs of a conventional three-phase-to-three-phase matrix converter are applied across the armature of a DC motor, and the field of the DC motor is connected from the third output thereof through phase-related diodes to respective phases of the input power lines. In accordance further with the invention, the diodes may be represented in a kit which is easily attached to a conventional three-phase-to-three-phase matrix converter, thereby adapting a converter for driving regenerative AC motors to a converter for driving regenerative DC motors.
The invention permits utilizing a standard regenerative matrix converter through a wide range of elevator drives, adapting the matrix converter for DC use with a simple diode kit, if desired, but otherwise using the matrix converter for an AC drive when appropriate.
Other objects, features and advantages of the present invention will become more apparent in the light of the following detailed description of exemplary embodiments thereof, as illustrated in the accompanying drawing.